As a further help in identification of these fifty trees in both summer and winter
condition, keys have been created.

A key is a scheme for easily and quickly identifying any unknown object under observation.
It is based usually on the most striking similarities and differences shown by the
various parts of the object. In trees, the leaves (plate 1)
have been selected for the summer key and the twigs and buds (plate
2) for the winter key because they present the most easily available parts of the tree
for showing differences and similarities.

Two alternative characteristics are presented.
These are the only choices possible. The two opposing characteristics are preceded
in the key by the same number (1 and 1 or 2 and 2) and are set at the same distance from
the left-hand margin of the page (when permitted on the screen). Often, 1 and 1 are
subdivided further into other groups on the basis of other differences; in every case,
however, the characteristics are opposed. If you find the desired characteristic in
the first group (1), there is no need to look in the second group, and study need be
confined to the subdivisions of the first group only.

The following example shows how to use the summer key. A branch with leaves is
examined from the tree in question. The leaves are broad so this falls under the
second step 1 (note that each number is in pairs, two 1's, two 2's and so on, and that
each step of a pair contains different characteristics or details). The twigs and
leaves are in pairs (opposite) so this leads to the choices under the first step 11 (if
the twigs were not opposite, second step 11, or alternate leaf arrangement would be
chosen). The leaves are compound (several leaflets on one stem) so the next clue is
in the first step 12. The leaflets have no stems, but sit tight on the main stem or
petiole of the leaf (second step 13). The tree is black ash.

Another branch, observed in late fall, has no leaves, and must be traced through the
second step 1 of the winter key. If the twigs have no pitchy taste or wart-like
branches found under the second step 2, but the buds and twigs are alternate, the second
step 3 must be selected. If there is no terminal bud, it is necessary to turn to the
first step 8. Close observation at the side or lateral bud may reveal many bud
scales which would lead to the second step 9. The buds are large and the twigs
lack thorns prompting the choice of the second step 11. At step 13, the choice is
the first alternate because the buds are "lopsided" and greenish-red. At
last the trail has ended with the name of the tree, which is basswood.

The most important distinguishing characteristics
of trees in the summertime are the form, arrangement, shape, and margin of the leaves.
In the wintertime, the size, color, and arrangement of the twigs are important, and
the position (terminal or not), size, shape, and color of the bud. Be sure you
thoroughly understand the illustrations in plates 1 & 2 and learn the distinctions before you attempt to use the key or go
into the field.

Once the name of the tree has been discovered in the key, you can find its description by
clicking on its name and number. For example, (6) Basswood is
linked to its complete description. If the description of the tree given does not
match the twig, trace the specimen again through the key. A small "clue"
may lead the "trail" in a new direction, and finally to the right tree.